a Motherboard with an Intel 865PE or 875 chipset
a P4 Processor above 2.4GHz with 800MHz FSB
At least 512MB of RAM at least PC3200 speeds. (Corsair XMS RAM is good stuff)
ATi Radeon 9600Pro (unless you want to go all out and get a 9800Pro)
SoundBlaster Audigy 2 Platinum Sound Card
Western Digital SATA Drive setup in RAID 0 (I have two 120GB 7200rpm SATA drive in RAID 0)
Lite-On optical drive are quality drives and inexpensive
And get a decent power supply.
Get a nice CRT monitor if you're gonna be gaming
and I decent set of speakers.